Extra fins, anyway… I think that the fins at the end are the vestiges of hind limbs.
The article says
Whale and dolphin fetuses also show signs of hind protrusions but these generally disappear before birth.Though odd-shaped protrusions have been found near the tails of dolphins and whales captured in the past, researchers say this was the first time one had been found with well-developed, symmetrical fins, Hayashi said.
Hat tip to P. Z. Myers at Pharyngula.
